Permeability Evolution of Pyrolytically-Fractured Oil Shale under In Situ Conditions

Fuke Dong, Zijun Feng, Dong Yang, Yangsheng Zhao, Derek Elsworth

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Abstract

In-situ injection of steam for heating of the subsurface is an efficient method for the recovery of oil and gas from oil shale where permeability typically evolves with temperature. We report measurements on Jimusar oil shales (Xinjiang, China) at stepped temperatures to 600C and under recreated in situ triaxial stresses (15 MPa) and recover permeability evolution with temperature and stress. Initial very low permeability evolves with the temperature above an initial threshold temperature at high rate before reaching a plateau in permeability above a peak temperature. The threshold temperature triggering the initial rapid rise in permeability is a function of triaxial stresses. For Jimusar oil shale, this threshold temperature ranges from 200C to 250C for burial depths of 500 m and from 350C to 400C for burial depths of 1000 m. This rapid rise in permeability correlates with the vigor of pyrolysis and directly scales with the production rate of pyrolysis-derived gas production. The permeability increases with temperature to a plateau in peak permeability that occurs at a peak-permeability temperature. This peak temperature is insensitive to stress and is in the range 450C to 500C for all Jimusar samples. Pyrolysis plays an important role in the stage of rapid permeability evolution with this effect stopping once pyrolysis is essentially complete. At these ultimate high temperatures, permeability exhibits little reduction due to stress and remains elevated due to the vigor of the pyrolysis. These results effectively demonstrate that oil shale may be transformed by pyrolysis from a tight porous medium into highly permeable medium and that oil and gas may be readily recovered from it.

Original languageEnglish (US)
Article numberen11113033
JournalEnergies
Volume11
Issue number11
DOIs
StatePublished - Nov 2018

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All Science Journal Classification (ASJC) codes

  • Renewable Energy, Sustainability and the Environment
  • Energy Engineering and Power Technology
  • Energy (miscellaneous)
  • Control and Optimization
  • Electrical and Electronic Engineering

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